fix(extension): harden chat and target tab lifecycle

extension/chat-format.test.mjs

@@ -19,4 +19,25 @@ describe('chat formatting', () => {
             { type: 'em', text: 'italic' }
         ]);
     });
+
+    it('splits up to 5000 Unicode code points into at most ten ordered chat-v1 messages', () => {
+        const split = globalThis.KoalaSyncChatFormat.splitChatText;
+        expect(split('hello world', 500, 10)).toEqual(['hello world']);
+
+        const emojiChunks = split('😀'.repeat(1001), 500, 10);
+        expect(emojiChunks.map(chunk => [...chunk].length)).toEqual([500, 500, 1]);
+
+        const maximumChunks = split('x'.repeat(5000), 500, 10);
+        expect(maximumChunks).toHaveLength(10);
+        expect(maximumChunks.every(chunk => [...chunk].length === 500)).toBe(true);
+        expect(maximumChunks.join('')).toBe('x'.repeat(5000));
+
+        expect(() => split('x'.repeat(5001), 500, 10)).toThrow(RangeError);
+    });
+
+    it('prefers whitespace boundaries without creating more chunks than the limit allows', () => {
+        const split = globalThis.KoalaSyncChatFormat.splitChatText;
+        const chunks = split(`${'a'.repeat(420)} ${'b'.repeat(179)}`, 500, 10);
+        expect(chunks).toEqual(['a'.repeat(420), 'b'.repeat(179)]);
+    });
 });